<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>京东三角形</title>
  <style>
    .jd {
      position: relative;
      width: 120px;
      height: 240px;
      margin: 100px auto;
      background-color: #aaa;
    }

    .jd span {
      position: absolute;
      right: 5px;
      top: -20px;
      width: 0;
      height: 0;
      border: 10px solid transparent;
      border-bottom-color: #aaa;
      line-height: 0;
      font-size: 0;
    }
  </style>
</head>

<body>
  <div class="jd">
    <span></span>
  </div>
</body>

</html>